1. Field of the Invention
The present invention is related to signal drivers.
2. Background Art
Signal driving systems on chips can be used to drive a signal (e.g., a current) through an internal or external termination (e.g., an impedance) in order to create a single-ended or differential output signal (e.g., a single-ended or differential voltage). Typically, a process is rated for a certain maximum supply voltage. Usually, a supply voltage is chosen that is smaller than a maximum allowed process voltage of the signal driving system (e.g., maximum breakdown voltage of devices in the signal driving system). However, some applications specifications for the signal driving system require the signal driving system to operate from a supply voltage that may be higher than the process rated voltage. For example, producing a differential output signal with a signal driving system may not possible when the maximum supply voltage is equal to or less than the common-mode output voltage that is determined by external sources.
For example, in some IEEE 1394 drivers, a process can be rated 2.5V, while the externally applied common-mode voltage at the output of the drivers can be as high as 2.515 Volts. In this case the signal driving system is unable to drive the differential output signal.
One way to overcome this problem is to choose a supply voltage above the common-mode voltage (e.g., about 3.3V for the above-mentioned IEEE 1394 driver). However, this could violate the process rating, which may damage the devices in the signal driving system. Damage to the devices in the signal driving system can result in failure of the signal driving system, costly repair and/or replacement costs, and downtime to perform the same.
Therefore, what is needed is a system and method that protect a signal driving system from being damaged by a power source having a value greater than a process rating.